Dave Hinz wrote:

On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:
Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.

Unfortunately, if you've tapped it, then you've lost the center. A
good approximation can be had this way:

Turn two buttons slightly smaller than 0.600 and with an ID that is a
close fit over your thread.

Turn two more buttons with a diameter of: 0.600*(SQRT(2))-D1

Where D1 is the diameter of the first two buttons.

Screw everybody down then remove all but the two smaller buttons.
Mount in a 4-jaw chuck. Indicate off each of the two smaller buttons
in turn and bore the two remaining holes.

George.

So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

Yes. But. You do get a tolerance stack up that way.

Wow, that metalwebnews.com site has some good info on it... time to
spend some quality reading time there.

Thanks,
Dave Hinz